This invention relates to turbine speed controllers and more particularly to a microprocessor-based turbine speed controller characterized by a set of permanently programmable memory devices contained therein.
The basic speed control of a turbine is usually accomplished by: monitoring the speed of a turbine employing a notched wheel attached to the turbine shaft and a magnetic pickup coupled adjacent thereto which generates a periodic time varying signal representative of turbine speed; subtracting said speed representative signal from a desired turbine speed signal to generate a speed error signal; and operating on said speed error signal with a dynamic controller to generate a signal which is used to position one or more fluid admission control valves to converge the speed of the turbine to that desired. In the late 50's and early to mid 60's, turbine speed controllers were comprised, for the most part, of a combination of analog and digital electronic hardware with a functional operation defined by a fixed hardwired structure. Problems with errors in speed control as a result of environmental changes, aging, and power supply variations were uncovered in the analog electronic hardware of these earlier hybrid systems. Consequently, some turbine speed controller manufacturers replaced the susceptible analog electronic hardware with digital electronic hardware. These all digital electronic type controllers, similar to that described in U.S. Pat. No. 3,802,188; by Barrett, issued Apr. 9, 1974, while overcoming the effects of environmental, aging and power supply variations, still maintained a fixed wired structure defining a particular operation.
As time passed, technological improvements in analyzing turbine systems lead to varying protective features in controlling the speed of the turbine. For example, measuring the temperatures of steam and metal at specific cross-sectional locations of the turbine during speed control operation was considered a viable method of establishing uneven heating of the turbine parts; the introduction of a mathematical rotor model established the possibility of calculating on-line the present and predicated stresses on the turbine rotor in accordance with certain measured parameters; and the capability of predicting the speed zones of vibration in accordance with steam conditions and blade design established the possibility of eliminating the danger of dwelling in these vibrating speed zones during speed control operation. These examples are just a few. Because some of these protective features are of paramount importance to the availability of the turbine operation, they have been required in some turbine installations. Speed control operational characteristics were varied, in many instances, from one turbine building block to another and from one turbine installation to another. The fixed wired speed controllers became costly to modify and expand to satisfy the protective requirements of a turbine installation.
About at this time, general purpose minicomputers were being introduced in the process control arena. Minicomputer-based turbine controllers, similar to that described in the copending application, Ser. No. 722,799; titled "Improved System And Method For Operating A Steam Turbine And Electric Power Generating Plant"; filed by Giras and Birnbaum on Apr. 4, 1968 and continued as Ser. No. 124,993 on Mar. 16, 1971 and Ser. No. 319,115 on Dec. 29, 1972, alleviated the problems of a fixed wired hardware structure by permitting turbine control operation to be characterized by a set of programs. Quite a few large turbine systems could justify the expense of a general purpose, minicomputer-based turbine controller because of the added features of automatic start-up, synchronization and automatic efficient load control afforded thereby. However, some municipalities and industrial complexes employ smaller turbines, on the order of 300 megawatts or less, which incorporate simple fluid admission control valving arrangements usually actuated by mechanical-hydraulic means as opposed to the large turbines, say 1,000 megawatts or greater, which use a variety of complex electrohydraulic actuated valving arrangements. These smaller turbines have generally been controlled by an operator using a basic fixed hardwired speed controller similar to the one previously described above. In these cases, the operator performs the protective control of the turbine, manually, according to a set of operational limitations provided to him by the turbine manufacturer.
Presently, there appears to exist a large gap in turbine speed control systems between the fixed hardwired speed controllers and the programmable minicomputer-based speed controllers. There are times when it is desirable to automatically protect the smaller turbine systems during start-up operations to ensure the availability and increase the economic efficiency thereof. To satisfy those small turbine system users who cannot justify the cost of a large programmable minicomputer-based speed controller, but find it desirable and request the ability to add, alter or modify certain protective features for their start-up operations, it may be advantageous to consider a turbine speed controller which consolidates the basic speed control functions in hardware, but allows programmable characterization of operation therein and is cost competitive with the fixed hardwired systems described above.
Additionally, the present programmable controllers of the type described in the application, Ser. No. 319,115 referenced to hereinabove, require special memory programming and loading techniques corresponding to the minicomputer associated therewith. Some even require power supply sequencing upon power turn-on and are susceptible to random electrical noise "spikes". These noise "spikes" may lead to a change in an instruction in the read/write memory contained in the minicomputer system which could cause an eventual shutdown of the turbine. It appears that a turbine control system which could fill the existing gap in turbine speed controllers and also provide for characterizing speed control operation as required while emulating a hardwired controller would reduce the probability of electrical noise shutdown thus increasing the availability of the turbine.